<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <lefter th:fragment="menu">
        <h3>我是左侧菜单</h3>
    </lefter>
</body>
</html>